The invention relates to a needle valve for a high pressure gas line including a housing with a stepping motor to which a needle is connected to be operated thereby for controlling the gas flow through a control passage extending through the housing.
For controlling the expansion valve of air-conditioning systems, it is known from EP 0 607 953 and WO 00/70276 to arrange the valve drive or a part of the latter, which is connected mechanically to the valve needle, in a housing part, which is connected to the housing including the valve in a gas-tight manner. This method of sealing off the inner region of the housing relative to the outside presumes that the parts of the valve drive, such as, for example, the armature winding of the latter, are not attacked by the medium flowing through the expansion valve. Moreover, a high pressure-resistant design of the drive housing requires a housing of appropriate strength.
It is known, furthermore, from U.S. Pat. No. 3,464,227 and U.S. Pat. No. 4,556,193, to connect the shank of the valve needle or of the closing body of an expansion valve of an air-conditioning system to the housing in a gas-tight manner via a bellows. A bellows-type seal however is suitable only for relatively low gas pressures and, to be arranged in the housing block of the needle valve, requires a relatively large space.
It is the object of the invention to provide a valve which is as small as possible, that is, a valve which is suitable for high pressures and has flow connections in two opposite directions and which can be used as an expansion valve of an air-conditioning system operated with carbon dioxide, that is to say for pressures up to 150 bar. Moreover, it should be simple in design, easy to manufacture, and easy to mount in the conduit system of a vehicle air-conditioning system.